ACPAtmospheric Chemistry and PhysicsACPAtmos. Chem. Phys.1680-7324Copernicus PublicationsGöttingen, Germany10.5194/acp-4-2353-2004Kinetic nucleation and ions in boreal forest particle formation eventsLaaksoL.1AnttilaT.13LehtinenK. E. J.1AaltoP. P.1KulmalaM.1HõrrakU.2PaateroJ.3HankeM.4ArnoldF.41Department of Physical Sciences, P.O. Box 64, FIN-00014 University of Helsinki, Finland2Institute of Environmental Physics, University of Tartu, 18 Ülikooli Street, Tartu, 50090, Estonia3Finnish Meteorological Institute, Air Quality Research, Sahaajankatu 20E, FIN-00880 Helsinki, Finland4Max-Planck-Institute für Kernphysik (MPI-K), D-6900 Heidelberg, P.O. Box 103980, Germany3011200449/1023532366This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.This article is available from http://www.atmos-chem-phys.net/4/2353/2004/acp-4-2353-2004.htmlThe full text article is available as a PDF file from http://www.atmos-chem-phys.net/4/2353/2004/acp-4-2353-2004.pdf

In order to gain a more comprehensive picture on different mechanisms behind
atmospheric particle formation, measurement results from QUEST 2-campaign
are analyzed with an aid of an aerosol dynamic model. A special emphasis
is laid on air ion and charged aerosol dynamics. Model simulations indicate
that kinetic nucleation of ammonia and sulphuric acid together with
condensation of sulphuric acid and low-volatile organic vapours onto
clusters and particles explain basic features of particle
formation events as well as ion characteristics. However,
an observed excess of negative ions in the diameter range 1.5-3nm
and overcharge of 3-5nm particles demonstrate that ions are also involved
in particle formation. These observations can be explained by
preferential condensation of sulphuric acid
onto negatively charged clusters and particles
and/or contribution of ion-induced nucleation on particle formation.
According to model simulations, which assume that the nucleation
rate is equal to the sulfuric acid collision rate, the relative contribution of ion-based
particle formation seems to be smaller than kinetic nucleation of neutral clusters.
Conducted model simulations also corroborate the recently-presented hypothesis according
to which a large number of so-called
thermodynamically stable clusters (TSCs) having a diameter between 1-3nm
exist in the atmosphere. TSCs were found to grow to observable sizes
only under favorable conditions, e.g. when the pre-existing particle
concentration was low.